Alan Grogono's Animated Knots offers clear instructions on how to tie all the knots you'll ever need, with photographic slideshows and browseable categories such as "climbing" and "scouting." The knot of the day is the Davy knot.
The Davy Knot was created in the 1950's by Davy Wotton when he was competing in the Welsh Fly-Fishing Team. He was experimenting to find a knot which he would be able to tie extremely quickly – which makes a lot of sense: less time tying knots equals more time catching fish.
The Ashley Book of Knots [Amazon] is the classic hold-in-your-hands volume on the matter, but it's in that curious hinterland where it's not old enough to be public domain but too old to be regularly printed, so is an unappetizing $55. And Ebay is only a little cheaper. Animated Knots is free of charge! Be sure to read the creator's family history page.
Tip: get a nice rope.